This study is exploring a new treatment called STX-478 for advanced solid tumors. Solid tumors are lumps of cancer cells, and advanced means they've spread a lot. The study is in two parts. Part 1 tests STX-478 alone, and Part 2 tests it with other cancer medicines, like fulvestrant, which is a hormone therapy. This study is open-label, meaning both doctors and patients know what treatment is being given. It's a Phase 1/2 study, which means it's early in research, focusing on safety and how the body processes the drug.

Participants need to be 18 or older, have a tumor with a specific genetic change (PI3Kα mutation), and be fit enough for treatment. They can't join if they have certain other health issues or have had recent cancer treatments.

• Duration: Each study part begins with a 28-day screening period, followed by treatment.
• Visits: Regular visits to the study site will be needed for monitoring.
• Risks: Potential side effects from STX-478 and other treatments.